Radio receiver



Jan. 6, 1942. E. F. ANDREWS 2,268;7 92

RADIO RECEIVER Original Filed April 8, 1933 3 Sheets-Sheet 1 I LNVENTOR Ga a/aid 2 area ream ATTORNEY.

Jan. 6, 1942, F, ANDREWS 2,268,792

RADIO RECEIVER Original Filed April 8, 1933 S Sheets-Sheet 2 INVENTOR. gain/a7 0 ant/WU;

$22M I ATTORNEY.

E. F. ANDREWS RADIO RECEIVER Jan. 6, 1942.

Original Filed April 8, 193:5

3 Shee ts-Sheet 3 IIIIHI INVENTOR. gain/amid? ana'eals', WV 7/9 ATTORNEY Patented Jan. 6, 1942 v RADIO RECEIVER Edward F. Andrews, Chicago, 1 11., assignor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Original application April 8, 1933, Serial No.

665,074, nowPatent No. 2,143,532, dated January 10, 1939. Divided and this application January 9, 1939, Serial No.'249,909

7 Claims. (01. 250-27) This application is a divisional from my copending application Serial No. 665,074, filed April 8, 1933, and issued on January 10, 1939, as United States Patent No. 2,143,532.

This invention relates to radio receivers'and has for one of its objects the provision of an improved radio receiver.

Among the other objects of the invention. are to provide a compact radio set with self-contained power supply. devices suitable for deriving filament and plate current therefor. from an automobile battery or from some other source of low voltage direct current, and to provide means for attenuating in the filament circuit of the radio set the high frequency disturbances occasioned by the power supply devices and exterior disturbances, such as those caused by the ignition system of an automobile, operated from the storage battery.

Other objects, advantages, and capabilities of my invention will appear from the following description of preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which Fig. 1 is a wiring diagram of one embodiment of the invention;

Fig. 2 is an illustration of a radio set embodying the invention, the main unit being shown in plan with its cover partly broken away and the remote control unit being shown in sectional elevation;

Fig. 3 is an end view of the remotecontrol unit,'

with its cover partly broken away; and v Fig. 4 is an elevation of the main unit, the cover being shown in section in order to display elements normally obscured thereby. j Referring more particularly to Fig. 2, it is to be noted that the main unit, which is designated by the reference numeral I0, is substantially similar in construction to the set described and claimed in my co-pending application, Serial No. I

639,821, filed October 27, 1932 Patent No. 2,103,135, granted December 21, 1937. This main unit is also shown in Fig. 4 and comprises a base I I which may be of inverted dish shape provided with an outwardly projecting flange I2 to which speaker, for example, by means of screws I9 which secure it to the edge of the speaker frame adjacent the periphery of the cone.

The central portion of the cover I8 is provided with openings 20 for the egress of sound from the speaker. The cover I8 is preferably of inverted dish shape and it extends downwardly towards the base II. The lowest portion of the cover I8 is of diameter somewhat larger than the base II so as to provide an annular opening side of the speaker cone. The base II serves to provide a mounting for radio apparatus such as radio tubes, transformers, a vibrator and the like, which will hereinafter be described in greater I detail. Such radio apparatus is located in a ring around the pot I5 of the loud speaker, being located within the annular space between the loud speaker and the cover I8. It will readily be understood that such radio apparatus may be rendered available for adjustment, replacement and the like by merely removing the cover I8, which may be done by taking out the screws I9.

Owing to the fact that it is preferred to tune the receiver in the remote control unit, it is not necessary to mount a variable condenser in'the main unit as in the case of the aforesaid copending application. The remaining radio apparatus is more convenient to this manner of assembly and the dimensions of the main unit may be somewhat reduced Energy is supplied to the main unit Ill by a cable I08. The main unit I0 is connected to the remote control unit 26 by means of a flexible cable 21 of suitable length. The number and relation of conductors in this cable depends upon the wiring system employed and will be discussed further in relation to the wiring diagrams shown in Fig. l.

The remote control unit 26 contains a thermionic tube 28 and a, variable condenser 29,

which usually comprisesfa plurality of units ganged together. The wiring diagram shown in Fig. 1 calls for a three-gang condenser. The

: condenser shaft 30 carries a pointer 3I which cooperates with a scale 32. The condenser shaft 30 is actuated from a control shaft 33 by means of friction wheels 34. At its outer end the condenser control shaft 33 carries a manual control knob-(n'0't shown) A manual volume control is provided in the remote control unit 26. This control may comprise a knob 35 and a rheostat or potentiometer 36 actuated thereby. The scale 32 may be provided with suitable indicia and is preferably translucent.

inside. The remote control also comprises a An incandescent lamp 31 is provided to illuminate the scale 32 'on the switch 38, the function of which will be more readily understood with reference to the wiring diagram shown in Fig. 1.

Referring -more particularly to the wiring diagram shown in Fig. 1, the receiver herein illustrated is a superheterodyne set of which the tube 28 in the remote control unit 26 is the oscillator and first detector. The tubes 39, and 4|, which are located in the main unit, are intermediate frequency amplifying tubes coupled by transformers tuned to the intermediate frequency. The tube 43 contains two diodes and a triode in the same envelope, all having a common cathode. 'One diode plate 94 serves as a second detector, the other diode plate 95 serves as a source of automatic volume control potential which is applied to the grid of tube 39, a portion thereof being applied to the grids of the tubes 4|! and 4|. The triode elements of the tube 43 serve as its first audio amplifier. The last tube 44 is an audio frequency power tube, the output of which is supplied to the voice coil of the loud speaker l6 through an output transformer 45.

The antenna conductor 45 preferably enters the cable 27 in or near the main unit and extends through the cable to the remote control unit 26, being connected therein to a primary coil 41 of the antenna input system which is of lower impedance than would be required to match the antenna employed, in view of the capacity through the cable. The conductor 48 preferably extends through the cable 21 within a grounded metal shield 93, for the purpose of preventing the antenna lead from picking up electrical disturbances. The coil 41 is inductively coupled to a coil 48, which is tuned by a condenser 49, one of the gang of condensers referred to generally by the reference numeral 29 in Figure 2. The coil 41' is connected to a point of the coil 48 comparatively near the grounded end thereof through a condenser 52, for the purpose of maintaining the impedance through the coil '48 lower than the total impedance of the coil. The coil 43 is inductively coupled to a coil 50 which is tuned by a variable condenser 5|, also one of the gang of condensers 29.

The coil is connected to the grid of the tube 28 and the plate of the tube 28 is connected in series with coils 53 and 54 and conductor 55 which extends through the cable 21. The coil'53 is coupled with the coil 55, which will be more fully described hereinafter. The coil 54 is coupled with coils 51 and '58. Coil 58 is tuned by condenser 53, which is the third of the gang of condensers designated 29. The output of the tube 28 energizes coils 54 and 58, which in turn energizes feed-back coil 51, causing tube 28 to oscillate. The result of this oscillation, in combination with a signal, is the production of current of intermediate frequency in coil 53, which in turn is communicated to coil 56 for transmission to the main unit.

The switch 38 is connected to conductors 6B and 6| which extend through the cable 21. The volume control 36 comprises a resistance 62, one end of which is grounded, and a conductive arm 63 which cooperates with said resistance. The arm 53 is connected to a conductor 64 which extends through the cable 21. The conductor 64 is connected through a low resistance 88 to the cathode of tube 4|. This cathode is also connected through a high resistance 39 to the screen voltage line 95. The cable 21 also includes a conductor 05 which supplies filament current from the main unit to the tube 28. Conductor 55, previously referred to, supplies B current from the main unit to the plate of the tube 28.

The remote control unit is preferably contained within a metallic housing 86 which is conductively connected to a ground conductor 61, which is preferably a metallic shield, extending between the remote control unit 26 and the main unit |0 through the cable 2'1. This shield contains the conductor 58 which carries the output from the coil 53 to a coil 69 in the main unit. The conductor 68 is connected to one end of the coil 56, the other end of this coil being grounded, preferably through the shield 61. The shield 61 effectively prevents any undesired signals from being picked up by the conductor 68 and introduced into the input of the intermediate frequency amplifying tubes 39, 40 and 4 I The main unit Ii! will now be described. The coil 69 is inductively coupled to the coil 10 which is connected to the input of the tube 39. The plate circuit of the tube 39 is coupled with the input of the tube 45. The plate circuit of the tube 40 is coupled with the input of the tube 4|. The plate circuit of the tube 4| is coupled to the detector 94. The detector produces a voltage drop across the resistor 95 and this voltage is impressed on the grid of the triode of the tube 43. The plate of the triode is resistance coupled to the grid of the tube 44. The coupling between the tubes 40 and 4| steps down the input to the latter tube. This is done in order to keep the grid swing of the tube 4| within satisfactory limits and to obtain the maximum gain which the permissible grid swing will permit ahead of the last intermediate stage, which is employed mainly for control purposes and additional selectivity.

The plate 95 provides the automatic volume control voltage, being connected by a resistance "13 to ground. This diode circuit includes the winding I02 which receives energy from the plate of the tube 43, being coupled to the primary of the transformer 99. The plate 95 is conductively connected through a part of resistance I03 and through a resistance |2| to the input of the tubes 40 and 4|, and through a suitable resistance I22 to the input of the tube 39.

The main unit It comprises an interrupter 14, a transformer 5, and a rectifier 16 which is associated with suitable filtering means including condensers 18 for the purpose of ironing out fluctuations in the direct current and potential delivered by conductor 19. This conductor is connected in known manner to the plate circuits of tubes 28, 39, 43, 4|, 43 and 44. The filament current for all the tubes is-derived from the battery 25 through conductor I99, which passes to the main unit Ill, and'is connected therein to the conductor 63. When the switch 38 is thrown to made position, the conductor It!) is connected to conductor 5| of the cable 2'! and to conductors 8| and 82 in the main unit It. The current for the filament of tube 28 fiOWs back to the control unit through conductor 65 of the cable 21.

The vibrator or interrupter 14 comprises a casing 84 including sound insulating material, in which is enclosed an electro-magnet '85 which controls points 83 in series with the winding of said magnet so as to cause continual interruption in the current flowin through the primary of the transformer 15. A condenser 8'! and high resistance 88 are provided both across the winding 85 and points 86.

It is to be noted that'one sideof the tube filaments is grounded and the other side of the filaments is connected to the line 8|, the filament of tube 28 being connected thereto by line 65 of cable 21, and the filament of tube I6 being connected thereto by line 82. Choke coils 9| are provided in th filament current circuit, being preferably arranged in series in the filament supply circuit, serving with the filament resistances to provide an induction-resistance filter which effectively filters out high frequency disturbances produced by the vibrator 14 and other causes. It will be seen that the filtering effect is greatest towards the input end of the receiving set, where any disturbance present would.

be amplified to the greatest extent.

The choke coil 92 is connected in.- series with the lead 55 which supplies plate current to' the tube 28. This chok coil prevents oscillation which might be caused by disturbances passing through lead 55, coil 53 and the plate ground capacity of the tube 28. I

It is preferred that the rectifying tube I6 passes current when the points 86 make contact, rather than when they break contact. The change from one condition to the other may be effected in many ways, one way being to reverse the connections of the secondary winding of the transformer I5. The set can thus be readily adapted for any automobile, regardless of which pole of the battery is grounded.

The triode elements of tube 43 act to amplify the output of the diode constituted by plate 94 and the cathode at audio frequency. The detected signal appears across the resistance 96 and is impressed upon the grid of the tube 43 through the filter resistor 91 and the capacity 98. The output transformer 99 of the tube 40 steps down the output of that tube and feeds a signal of reduced amplitude to the grid of the tube 4| by means of the winding I00. This winding may be tuned to the intermediate frequency for additional selectivity. Thus there is little or no over-all gain from the last intermediate stage of amplification, including the tube 4|. Certain desired results are attained by thus stepping down the output of the tube 40 into the tube 4|. In the first place, excessive difference of potential between the diode plates 94 and 95, which might cause oscillation in the tube 4|, is avoided. In the second place, the grid swing of the tube 4| is kept relatively small. In the third place, by taking practically all the gain in the first intermediate frequency tubes, substantially the maximum gain is available in the plate circuit of the tube 40, which is the source of automatic volume control energy. Any gain taken in the tube 4| would not add anything to the automatic volume control voltage. The tube 4| is of the variable mu type so that a large variation of the potential difference between the cathode and the grid may be employed to give the desired range of volume control.

Even when a variable mu tube is employed, it is desirable to limit the grid swing to avoid distortion. This is accomplished by impressing a stepped-down sign-a1 to the grid of tube 4|, as previously described. The signal is then amplified up again to the desired value in the tube 4| and the transformer IOI, from which it is impressed upon the diode plate 94, which acts as the second detector. The transformer 99 includes a secondary winding I02 which supplies potential to the diode plate 95 which is rectified and appears across the resistance I03. This direct-,1 current potential is utilized for automatic volume control, as previously described. I

The field of the loud speaker comprises two windings I04 and I05. The winding I04 is connected in series with the plate voltage supply from the secondary of the power transformer I5 through the rectifier tube I6. The winding I04 acts as a choke coil to filter the plate supply, as well as supplying part of the energy to the speaker field. Only a part of the speaker field energy is supplied from the plate supply, the remainder for bringing the speaker to the proper sensitivity being supplied directly from the battery to the coil I05. By properly proportioning these coils, the speaker field can be employed as a choke coil and th proper speaker sensitivity attained with a vibrator of moderate output.

To avoid operating the vibrator without a load, it is desirable that the filaments of the tubes should have attained their operating temperature before the vibrator is connected to the battery. A thermostatic relay I06 fulfills this purpose. This relay is adapted to be operated by aheating winding I0I which is connected to conductor 82 and energized upon the closing of I the switch 39. The winding I0'I is in parallel with the filaments of the tubes and the current therefor is derived from the battery. The thermostatic relay is proportioned to close the vibrator circuit after the cathodes have attained operating temperature The thermostatic switch is preferably temperature compensated so that its time interval is not excessively affected by changes in atmospheric temperature.

The thermostatic relay serves both as a delayed switch and as a remotely controlled relay. The vibrator current does not pass through cable 21, thus reducing the liability of the introduction of undesirable electrical disturbances into the amplifier tubes, and also avoiding the larger conductors or higher voltage drop which would be occasioned by a higher current through the cable.

The battery cable I08 comprises three leads I09, H0 and III, surrounded by a shield II2,

one end of which connects to the chassis of the main unit, and the other to the grounded terminal of the battery. The conductor I09 is connected to the ungrounded terminal of the battery and leads to the switch 38 for the filament and heating element I0'I supply. Conductor H0 is connected to the positive terminal of the battery and leads toone contact of the thermostatic relay I06, through which it is connected in parallel through the primary winding of the transformer I5 and vibrator I4 on the one hand, and through coil I05 on the other hand, to conductor III which is connected to the negative terminal of the battery. In Fig. 1 I have shown the negative terminal of the battery to be grounded.

Should the automobile be one in which the positive terminal is grounded, then shield H2 and conductor I I0 should be connected to the positive terminal of the battery, and conductors I09 and III should be connected to the negative terminal of the battery. It is to be noted that this hook-up follows the nomenclature of the preceding paragraph, according to which shield H2 is grounded and conductor I09 is connected to the ungrounded terminal, and lead H0 is connected to the positive terminal, while lead I II is connected to the negative terminal.

It should be noted that in the embodiment of the invention illustrated, the conductors H and I I I run to the primary of the transformer I5 and to one side of the vibrating interrupter contacts 86, respectively, thus forming an interrupter circuit. The conductor I09 and the grounded shield I08 connect to the ungrounded and the grounded sides of the filaments respectively, thus forming a filament circuit, which is separate from the interrupter circuit, up to the terminals of the battery 25. The choke coils 9| are in series with the conductor I09, which forms the ungrounded side of the filament circuit. These choke coils serve to attenuate any high frequency disturbances caused by the interruption of the current in the interrupter circuit by the contacts 80 or which may be impressed on the battery from other sources, such, for instance, as the ignition system of the automobile. The complete separation of the filament circuit from the interrupter circuit, apart from the battery, which is common to :both circuits, reduces the coupling between the circuits and consequently reduces the introduction of undesired high frequency disturbances into the filament circuit. The choke coils SlI are preferably located in the ungrounded side of the filament circuit between the filaments and the portion of the circuit carrying current from the battery to the interrupter, as shown in Fig. 1. Owing to the low degree of coupling between the filament circuit, on the one hand, and the interrupter and other circuits which may be connected directly to the battery, on the other hand, and owing to the choke coils 9|, the amount of disturbance which reaches the filaments is very greatly attenuated, and noise in the loud speaker due to such disturbance may be almost completely eliminated.

The operation is as follows: The switch 38 being closed, the circuits through the filaments and the element I0! are made. By the time the filaments have attained their operating temperature, the thermostatic switch I06 has closed, completing the circuit through the vibrator I4 and the primary of the plate supply transformer I5, as well as through the field coil I05. An interrupted current passes through the primary of the transformer 15. The voltage of this current is stepped up in the secondary of the transformer and is rectified in tube I6 so as to provide B voltage by means of conductor I9. The field winding of the speaker I6 is energized and the desired station can be tuned in by actuating the gang of condensers 29. The volume level control 63 adjusts the relative grid bias of tube 4| by making the cathode more or less positive. It is to be noted that this control in the main unit is effected from the control unit by variation of a direct current which is of practically constant value for any particular manual setting of the volume level control 63.

The automatic volume control voltage is applied to the grids of the tubes 39 and 40, which elements are ahead of the source of energy from which the automatic volume control voltage is derived, which source is the plate circuit of the tube 40. Automatic volume control. voltage is also applied to the grid of the tube 4|, which is after the source of the energy which supplies the automatic volume control voltage which, as has been noted, is the plate of the tube 40. It may here be pointed out that the effective automatic volume control voltage applied to the tubes be fore the source of the automatic volume control energy is to decrease the gain of these tubes, and hence the automatic volume control voltage produced, sothat these tubes provide only a diminishingcorrective effect. However, the application of automatic volume control voltage to the grid of a tube after the source of automatic volume control energy, such as tube 40, produces a reduction of gain without any reduction of the automatic volume control voltage. By tapping in the, grid connection of the tube 4| at a suitable point on the resistor I03, signals of substantially uniform strength can be obtained from divers stations with antenna signals of widely different power. Indeed, by suitable adjustment of the connection of the grid 4| to the resistor I03, it is possible to make a stronger antenna signal appear as a weaker audible signal than that derived from a weaker antenna signal.

It is not intended to limit the invention to automobile radio receivers, since it may be applied to home sets and indeed to any manner of radio set.

Although the invention has been described in connection with the specific details of preferred embodiments thereof, it must be understood that such details are not intended to be limitative of the invention, except insofar as set forth in the following claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent of the United States is:

1. In a battery operated radio receiver, a plurality of thermionic tubes each of which is provided with a filament having a pair of terminals, means for grounding one terminal of each of said filaments, a B-supply transformer having a primary winding and a secondary winding, a low voltage battery having two terminals, an interrupter for rendering the current from said battery transformable connecting said primary winding to said battery to form an interrupter circuit, means for grounding one side of said circuit, a housing in which all of the foregoing elements excepting the battery are located, means for grounding one of said battery terminals, said battery being located externally to said housing, conductive means connecting together the grounded terminals of said filaments, the grounded side of said interrupter circuit, and the grounded terminal of said battery, a conductor extending from the other side of said interrupter circuit to the ungrounded terminal of said battery, a separate conductor extending from the ungrounded terminals of said filaments to the ungrounded terminal of said battery, and a low resistance, high frequency choke coil in said last conductor.

2. In a battery operated radio receiver, a plurality of thermionic tubes having filaments connected in parallel, a B-supply transformer having a primary winding and a secondary winding, a low voltage battery having two terminals, an interrupter for rendering the current from said battery transformable connected to said primary winding to form an interrupter circuit, a housing in which all of the foregoing elements excepting said battery are located, conductive means connecting together one side of said filaments, one side of said interrupter circuit, and one terminal of said battery, a conductor extending from the other side of said interrupter circuit to the other terminal of said battery, a separate conductor connecting all of the other sides of said filaments together and to the last mentioned terminal of said battery, a low resistance, high frequency choke coil in said last named conductor, and at least one low resistance, high frequency choke coil connected in series with said last named conductor between two of said filaments.

3. In a battery operated radio receiver, a plurality of thermionic tubes having filaments connected together to form a filament circuit, a B- supply transformer having a primary winding and a secondary winding, a vibrating interrupter connected to said. primary winding to form an interrupter circuit, a housing in which all of the foregoing elements are located, a pair of terminals adapted to have a low voltage battery connected across them, conductive means connecting together one side of said filament circuit, one side of said interrupter circuit, and one of said pair of terminals, a conductor extending from the other side of said interrupter circuit to the other of said pair of terminals, a separate conductor extending from the other side of said filament circuit to the last mentioned one of said pair of terminals, and a low resistance, high fre-.

quency choke coil in said last named conductor, said choke coil being located within said housing. 4. A battery operated radio device comprising a plurality of thermionic tubes having filaments connected together to form a filament circuit, a B-battery transformer having a primary winding, a low voltage battery having two terminals and a secondary winding, an interrupter for rendering the battery current transformable connected to said primary winding to form an interrupter circuit, a housing in which all of the foregoing elements excepting the battery are located, said battery being located externally to said housing, conductive means connecting the two sides of the interrupter circuit to the two terminals of the battery, conductive means separate from said first conductive means connecting the two sides of said filament circuit with the two terminals of the battery, and at least one low resistance, high frequency choke coil in said last named separat conductive means. 5. In battery operated radio receiving apparatus, a plurality of thermionic tubes each of which is provided with a filament having a pair of terminals, means for grounding one terminal of each of said pairs of filament terminals, a B- supply transformer having a primary winding and a secondary winding, a circuit interrupter having a pair of terminals, means for connecting one of said circuit interrupter terminals to one end of said primary winding, a low voltage battery having a pair of terminals, conductive means for connecting the other of said interrupter terminals to one of said battery terminals, conductive means for connecting the other battery terminal to the other end of said primary winding, a separate conductive means for connecting said last named battery terminal to the ungrounded terminals of said filaments, a shield for said three conductive means, one end of said shield being connected to the grounded terminals of said filaments and the other end of the shield being connected to said first named battery terminal whereby said shield forms part of the battery energizing circuit for said filaments.

6. In a battery operated radio receiver, a thermionic tube provided with a filament having a pair of terminals, means for grounding one of said filament terminals, a B-supply transformer provided with at least three internal conductors,

means connecting one of said conductors between the other of said interrupter terminals and one of said battery terminals, means including another of said conductors for connecting the other battery terminal to the other end of said primary winding and means including the third conductor for connecting said last named battery terminal to the ungrounded terminal of said filament, said last named means including a low resistancehigh frequency choke coil in series with said third conductor, and means for connecting the shield of said shielded cable between the grounded terminal of said filament and the first named battery terminal.

7. The arrangement described in the next preceding claim wherein a second thermionic tube is provided, said second tube having a filament 

